Odors from utility-room floor drain

Q. There has been a very unpleasant sewer-like odor coming from the floor drain in my utility room. We have a 19-year-old tri-level with a basement; the utility room is one level up from the basement. Nothing ever drains into this drain, so the water just sits in the trap and becomes very dark brown/grey and mucky-looking.

The problem seems to be isolated to this one drain; we have a similar floor drain in the basement into which the A/C pipe drains, but that water is clear and odor-free.

I poured a quart of hydrogen peroxide into the smelly drain, allowed it to sit overnight, and flushed it with water. After repeating this process the next day, the water in the trap was a nice, clean color and the smell was gone. However, after two weeks, the smell is starting to come back and the water is turning brown again.

Any idea what could be causing this odor? It’s not a dry trap; there is always water in it, albeit smelly and brown. Instead of doing weekly flushings, do you have suggestions to permanently get rid of the smell? Do you have any preventive maintenance recommendations to keep my tubs, showers, sinks and other drains nice and clean, and odor-free?

Fortunately the only one that smells is the one in the utility room, but I would like to stay ahead of the game with the other drains.

A. The water in the utility room drain is turning brown and getting mucky because the cast-iron floor drain is rusting — a common problem. Stagnation will also cause unpleasant odors.

The solution is to change the water on a regular basis by pouring fresh water down it. Instead of peroxide, you can use a small amount of household bleach in the trap once a week to keep it odor-free, but that will not help with rusting.

As for preventive maintenance, I recommend a monthly flushing of all the traps of the house fixtures with Super Washing Soda, following the instructions on the side panel of the big yellow box. You should be able to buy it in the cleaning supplies section of supermarkets.